Visible crew/equipment: In the scene where Brody approaches the group of teenagers on their smashed boats, the angle cuts to show Brody approaching seen as if from Cable Junction. At this point, there is a huge mistake. The teenagers' boats are clearly visible in the foreground, the kids have all completely vanished, and you can spot the cameraman standing on the boats quite clearly.
Revealing mistake: When the teenage guy is getting attacked by the shark, the shark slams him up against the boat. He attempts to climb back on the boat and the shark pulls him down and the guy rips some wood from the edge of the boat. You can see the cut away part of wood that will be ripped off before he actually rips it off.